I've read manuals that stated a 45 degree temperature drop is normal and acceptable; however, I don't buy that at all.
My feeling is that the outlet temps should be down in the high 30s/very low 40s at a minimum on a 90 degree day.
Some years back on my now gone Mercury I had the A/C on that one putting out 25-30 degree air on a 100+ degree day although I consider this one more of an anomaly.
The best thing that can be done is to connect a full gauge set and see what's going on with the pressures on both the high and low sides. If the pressures are fine then one should consider the possibility of a blend door not functioning correctly.
You might also raise the hood and look at the evaporator outlet fittings, the accumulator, etc. for condensation. If there's any humidity to speak of you should see these parts sweating and there should be a constant condensation drip under the car if the A/C is functioning even halfway like it should.